1. Field of the Invention
The present invention relates to fluid displacement apparatus and, more particularly, relates to a variable displacement mechanism of a refrigerant compressor for an automotive air conditioning system.
2. Description of Related Art
Refrigerant compressors with a variable displacement mechanisms are used in automobile air condition. A known refrigerant compressor with a variable displacement mechanism is described in Japanese Patent No. H4-74549.
A refrigerant compressor may be a wobble plate-type compressor with a variable displacement mechanism and may include a compressor housing enclosing a crank chamber. A rotor is located in the crank chamber and is attached to a drive shaft. A slant plate is attached to the rotor by a hinge mechanism. The drive shaft penetrates the slant plate, which is attached to a sleeve. The drive shaft is surrounded by the sleeve. A space is formed between the outer surface of the sleeve and the inner surface of the slant plate such that the slant plate has a slant angle for the drive shaft. The hinge mechanism allows the slant angle to be varied with regard to the drive shaft.
A wobble plate is located on the slant plate through a bearing. A plurality of piston rods are connected to the wobble plate. The piston rods have piston members which are located in cylinder portions formed in the compressor housing. The cylinder portions are formed in the compressor housing at specified intervals so as to surround the driving shaft. A guide rod is supported by the compressor housing and is parallel to the drive shaft in the crank chamber. The wobble plate is slidably attached to the guide rod.
The rotor is rotated by the rotation of the drive shaft. Because the slant plate is connected to the rotor by the hinge mechanism, the slant plate is rotated in accordance with the rotation of the rotor. With the rotation of the slant plate, the wobble plate wobbles or oscillates, and the slidably attached guide rod and piston members are reciprocated in the cylinder portions.
The compressor housing has a suction chamber and a discharge chamber. The chambers are in communication with the cylinder portion. When the piston members are reciprocated in the cylinder portions, refrigerant is taken from the suction chamber into the cylinder portions and compressed. The compressed refrigerant is discharged as a discharged gas into the discharge chamber. Because the slant plate has the variable slant angle discussed above, the stroke of each piston member varies according to the slant angle. Therefore, the compressor varies its compression capacity in relation to the variable slant angle.
First and second communication paths may be formed in the compressor. The discharge chamber communicates with the crank chamber via the first communication path. The compressor further comprises a switching valve that opens and closes the first communication path and may set the suction pressure to a predetermined level.
The crank chamber communicates with the suction chamber via the second communication path in the compressor. When the compressor has been dormant for a period of time, liquid refrigerant may exist in the low pressure side of a refrigeration circuit. This event may occur because the refrigeration circuit is connected to the compressor. Thus, the liquid refrigerant flows from the refrigeration circuit into the crank chamber through the suction chamber. More specifically, liquid refrigerant flows into the crank chamber from the suction chamber when the temperature in the engine compartment is low, such as prior to starting the automobile.
When the compressor commences operations, the opening area of the second communication path corresponds to the amount of the liquid refrigerant that exists in the crank chamber. Consequently, there is a pressure difference between the crank chamber and the suction chamber. The variable slant angle becomes a predetermined minimum angle, so that the compressor has a minimum compression capacity. Thus, it is difficult to obtain a desired compression capacity until the liquid refrigerant is sufficiently removed from the crank chamber. Therefore, the desired compression capacity may be difficult to obtain in the compressor during initial operations.